12 NATURE OF CARBOHYDRATES 



economy of this world of ours. It will be seen that this tissue 

 not only keeps the air in a wholesome condition for breathing 

 and so makes life possible upon the earth but that all animal life 

 is absolutely dependent, either directly or indirectly, for food 

 upon the products built up by the chlorenchyma. Let us see 

 how these foods are formed. Various substances are absorbed 

 by the roots, and the vascular bundles, which extend throughout 

 the plant body, transfer them to the chlorenchyma. This ab- 

 sorbed material is in large part water, but various mineral sub- 

 stances are dissolved in it. Various gases, as carbon dioxide, 

 also find their way through the stoma to the chlorenchyma. All 

 of these absorbed substances are composed of elements. Thus 

 water consists of two elements, hydrogen and oxygen, in the pro- 

 portion of two parts of hydrogen to one part oxygen. This com- 

 position is indicated by the abbreviation, H2O. So the gas, 

 carbon dioxide, contains one part of carbon and two parts of oxy- 

 gen, indicated thus CO2. Chloroplasts have the power under 

 suitable conditions of decomposing or tearing apart these com- 

 pounds and of reuniting their elements into new compounds that 

 are quite different from the original ones. In this way CO2 

 and H2O are decomposed and the elements reunited into complex 

 compounds or foods consisting of carbon, hydrogen and oxygen. 

 Such complex foods as cane sugar, consisting of twelve parts of 

 carbon, twenty-two of hydrogen, and eleven of oxygen are formed 

 in this way. This very common food is expressed by the formula 

 C12H22OU. So also other foods are formed, as grape sugar 

 C6Hi20(; and starch usually indicated as some multiple of CeHioOs. 

 The cellulose walls of the parenchyma cells have the same com- 

 position as starch. It will be seen that all these foods have 

 carbon united to hydrogen and oxygen in the same proportion 

 as it exists in water. Cane sugar has carbon united to eleven 

 times H2O, and starch five times H2O. It was supposed that 

 these substances were a combination of carbon and H2O. For 

 this reason they were called carbohydrates. This name is still 

 applied to these foods although it is known that the base is not 

 H2O but the hydroxyl OH. The actual changes that are effected 

 in the formation of these various carbohydrates are not known. 



